Magnetic bearing



March 19, 19 68 s, WE|NBERGER 3,374,037

MAGNETIC BEARING Filed Dec. 21, 1964 Fig 2 54 INVENTOR.

SANFORD M. WEINBERGER /7% MHZ W AGENT United States Patent 3,374,037MAGNETIC BEARING Sanford M. Weinberger, Philadelphia, Pa., assiguor toGeneral Electric Company, a corporation of New York Filed Dec. 21, 1964,Ser. No. 420,024 4 Claims. (Cl. 308-10) This invention pertains to theart of bearings or other supports which prevent or limit translation butpermit rotation. More particularly, it pertains to the use of magneticfields to limit or oppose displacement of a body from a centrallocation.

In many arts it is desirable to support or center one piece with respectto another while still permitting it to move in ways such as rotationwhich do not impair the centering; and it is particularly desirable todo this with no or minimal static friction. It has often been proposedto employ magnetic forces to do this. In particular, the forces ofmagnetic attraction are desirable because they are of very considerablemagnitude; for example, permanent magnets can support their own weight.Unfortunately, the inverse square law of force between magnetic polesand its more sophisticated and accurate substitutes alike indicate thatit is not possible to achieve stable equilibrium by simply usingmagnetic attraction of permanent magnets to hold a ferromagneticarmature in a central position. If such an armature were placed in aneutral position, a slight displacement would increase the attraction ofthe pole approached by the armature and decrease the attraction of thepole from which the armature was moving away; this is just the oppositeof the behaviour required for stability. An armature having apermeability less than that of free space, that is, a diamagneticarmature, will tend to move to a stable central position in a suitablyshaped magnetic field. Unfortunately, the central forces developed bysuch a device are proportional to the amount by which the permeabilityof the diamagnetic material is less than that of free space. Thisquantity is very small. A bearing employing such material is the subjectof application Ser. No. 367,307 entitled Diamagnetic Bearing, filed Apr.24, -1964, by Davis and Weinberger, and assigned to the assignee of thisapplication.

I have invented a bearing or position-seeking or centering deviceemploying a material having a permeability greater than that of freespace to produce magnetic suspension or centering. This invention may beunderstood by considering a symmetrical permanent magnet immersed in afluid magnetic medium having a permeability 5 greater than that of freespace. If the fluid medium is surrounded by a nonmagnetic container notmuch larger than the magnetic itself, the magnet will tend to orientitself so that the total energy stored in the magnetic field in themedium is a maximum. Such energy will, in general, be a maximum if themagnet is centered in the container. Since the magnetic medium is fluid,the magnet may be displaced from the central position at low speeds withno frictional resistance; but since the displacement will reduce thetotal magnetic energy stored in the medium, there will be a restoringforce tending to return the magnet to its central position. It should beobserved that linearity of the magnetic characteristics of the magneticfluid will not impair the operativeness of my invention; it is notnecessary that the fluid be subject to saturation in order for the totalstored magnetic energy to be reduced by displacement of the system fromits equilibrium point.

Thus, a general object of my invention is to provide a stable bearing orposition-seeking device employing magnetism and a medium havingpermeability greater than "ice that of free space. Achievement of thisgeneral object will produce other beneficial results, such as lowfrictional resistance to movement, simplicity, economical design, andother objects discernible to those skilled in the art after they haveknowledge of my disclosure.

For the better explanation and understanding of my invention, I haveprovided figures of drawing, in which:

FIG. 1 represents a simple embodiment of my invention particularlyuseful for exemplifying its underlying principles; and

FIG. 2 represents an embodiment of my invention applied to support asmall anemometer movement suitable for measuring very slow air flow byvisual counting of the revolutions.

Considering FIG. 1, there are represented two horseshoe magnets 10 and12 rigidly connected with each other by a tie bar 14 of non-magneticmaterial having a distal terminal eye 16. Magnets '10 and 12 arerepresented as immersed in a solution 18 of permeable magnetic fluidwhich may consist of'an aqueous solution grams of hydrated ferrouschloride FeCl- .4H O in 400 milliliters of water. Such a solution isknown to be paramagnetic. Surrounding the magnets 10 and 12 andcontaining the magnetic fluid 18 is a vessel 20, here represented insection, which may be a conventional chemical laboratory glass beaker.The eye 16 of tie bar 14 is represented as connected by a book 22 to anarm 24 which is balanced upon a knife edge bearing 26, and whichcarries, by means of a hook 28 a balance pan 30 represented ascontaining two weights 32 and 34, respectively. The value of the weights32 and 34 is such as approximately to balance the immersed weight of themagnets 10 and 12 and the weight of tie bar 14 so that gaps 36 and 3 8exist between the poles of magnet 12 and the upper surface of fluid 18,and between the poles of magnet 10 and the lower boundary of fluid 18,respectively. Assuming magnets 10 and 12 are alike in size, shape andmagnetic characteristics, the total magnetic energy stored in fluid 18will be a maximum when the length of the (double) gap 36 is equal to thelength of the (double) gap 38. Consequently a small verticaldisplacement of tie bar '14 will alter the sizes of the gaps in such away that there will be a net magnetic force tending to return the tiebar to such a position that the gap lengths will again be equal.

FIG. 2 represents a more general embodiment of my invention which isadapted not merely to resist displacement on one dimension, but in allthree. Three horseshoe magnets 40, 42 and 44 are represented mountedaround the periphery of a circle, with their poles facing out. Forsymmetry, a fourth magnet 45 is located diametrically opposite magnet 44and thus, in orthographic projection, is concealed by it. Horseshoemagnet 46 is located with its poles pointing upward. Similarly a lowerdeck of magnets comprises peripherally mounted magnets 48, 50, 52 and 53mounted with their poles facing out, magnet 53 being locateddiametrically opposite magnet 52 and thus being concealed by the latter.Magnet 54 is located with its poles pointing downward. The structurewhich supports the magnets in these relationships is designatedgenerally by reference number 56; it may be of any material, preferablynonmagnetic, having suitable mechanical properties. A stub shaft 58rises from structure 56 (conveniently, through a hole in magnet 46) andcarries an anemometer 60. It is desirable to provide a float 62 tocounteract in part, by its buoyancy in magnetic fluid 64, the weight ofthe assembly. As may be seen, the walls of container 66 (representedsimply as a beaker) fit sufficiently closely around the pole faces ofmagnets 40, 42, 44, 45, 48, 50, 52 and 53 so that a slight lateraldisplacement of the structure (or a slight rotation around a hori-Patented Mar. 19, 1968 4 zontal axis) will alter the volume of magneticfluid lying between the pole pieces of at least some of the magnets, andwill thus alter the stored magnetic energy of the system. Thisalteration will produce a force tending to undo the displacement.Magnets 46 and 54 will act to check vertical displacements similarly tomagnets 12 and 14 in the embodiment represented in FIG. 1. Thus theentire assembly will tend to remain centered and upright in beaker 66.Light breezes on anemometer assembly 60 will be able to rotate itslowly, since there are no static frictional forces to require a minimumbreak away torque before the assembly can rotate. The anemometer is,.ofcourse, simply a convenient example of a device which can benefit by theuse of my invention.

While my examples have been of a common and readily availableparamagnetic solution, any ferromagnetic fluid if it is homogeneous maybe used also. Thus a colloidal suspension of finely dividedferromagnetic particles, if it is sufliciently stable as a colloid sothat application of a magnetic field will not cause segregation orlocking together of the magnetic particles, may be used as the magneticfluid specified. My use of the term magnetic fluid thus implies only apermeability greater than that of free space. US. Patent 2,667,237, atcolumn 3, lines 39 through 47 thereof, says:

Magnetiza'ble liquids, particularly a liquid of this nature in which asmall quantity of iron is mixed in mercury are known. It is also knownthat these earlier magnetic liquids were so designed that the physicalproperties of the material did not change under the influence of amagnetic field; such magnetic fluids were designed solely to respondpositionally to the influence of a proximate magnet.

The same patent describes a novel material of completely difierentproperties with the statement: The effective viscosity of the fluid willbe found to increase (with a properly constituted fluid) as the magneticfield intensity is increased. The older, conventional material may beditferentiated by being described as having viscosity and fluiditysubstantially independent of any magnetic field applied to it.

In a technique so broad as the one I here disclose, there are naturallymany possible variations, particularly of geometry. The basic criterionwhether a given geometry will produce stable centering is that themagnetic energy stored in the device be a maximum in the desiredorientation, and therefore, be reduced by any displacement.

The subdivision of the appended claims into subparagraphs is purely forease in reading and not indicative of any necessary relation or relativeimportance of the elements recited.

What is claimed is:

1. A position-seeking device comprising:

a source of magnetomotive force having magnetic poles;

a magnetic fluid whose viscosity and fluidity are substantiallyindependent of any magnetic field applied to it surrounding the saidpoles;

container means bounding the same fluid and generally conforming to theshape of the said source of magnetomotive force.

2. A position-seeking device comprising:

a permanent magnet having poles;

a magnetic fluid whose viscosity and fluidity are substantiallyindependent of any magnetic field applied to it surrounding the saidmagnet;

a container providing a fluid boundary to form in the fluid symmetricalpaths between the poles.

3. A position-seeking device comprising:

a central frame holding a plurality greater than two of horseshoemagnets symmetrically arranged at a first level with their poles facingoutward,

a plurality greater than two of horseshoe magnets arranged at a secondlevel with their poles facing outward,

a container having central internal symmetry, containing the saidpluralities of horseshoe magnets with gaps between the poles of the saidhorseshoe magnets and the walls of the said container, and containing amagnetic fluid sufficient in volume to immerse the said pluralities ofhorseshoe magnets.

4. A position-seeking device as claimed in claim 3, in

which there are mounted on the said central frame a horseshoe magnethaving its poles facing upward,

and

a horseshoe magnet having its poles facing downward.

References Cited UNITED STATES PATENTS 2,575,360 11/1951 Rabinow192-21.5 2,667,237 1/1954 Rabinow 192-21.5 2,806,533 9/1957 Fleck19221.5 2,896,931 8/1959 Didszuns 192-21.5 2,903,109 9/1959 Didszunsl9221.5 2,983,349 5/1961 Meiklejohn 192-21.5 3,250,341 5/1966 Takahaski192-215 DAVID X. SLINEY, Primary Examiner.

J, W. GIBBS, L. L. SMITH, Assistant Examiners.

1. A POSITION-SEEKING DEVICE COMPRISING: A SOURCE OF MAGNETOMOTIVE FORCEHAVING MAGNETIC POLES; A MAGNETIC FLUID WHOSE VISCOSITY AND FLUIDITY ARESUBSTANTIALLY INDEPENDENT OF ANY MAGNETIC FIELD APPLIED TO ITSURROUNDING THE SAID POLES; CONTAINER MEANS BOUNDING THE SAME FLUID ANDGENERALLY CONFORMING TO THE SHAPE OF THE SAID SOURCE OF MAGNETOMOTIVEFORCE.